Development of a Mechanism for Nitrate Photochemistry in Snow

Bock, Josué; Jacobi, Hans-Werner

doi:10.1021/jp909205e

Cited by 42 publications

(46 citation statements)

References 64 publications

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“…Nitrate ion photochemistry has been proposed to be a major source of OH and NO x in snowpacks. 30,[38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]137 Sea salt aerosols are also deposited on the snowpack and can become concentrated in a quasi-liquid layer (QLL) on the surface. [138][139][140] Based on the present results, halide ions could significantly impact nitrate photochemistry via enhanced nitrate ion concentrations at the interface of this QLL.…”

Section: Discussionmentioning

confidence: 99%

Production of gas phase NO2 and halogens from the photolysis of thin water films containing nitrate, chloride and bromide ions at room temperature

Richards-Henderson

Callahan

Nissenson

et al. 2013

Phys. Chem. Chem. Phys.

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aNitrate and halide ions coexist in particles generated in marine regions, around alkaline dry lakes, and in the Arctic snowpack. Although the photochemistry of nitrate ions in bulk aqueous solution is well known, there is recent evidence that it may be more efficient at liquid-gas interfaces, and that the presence of other ions in solution may enhance interfacial reactivity. This study examines the 311 nm photolysis of thin aqueous films of ternary halide-nitrate salt mixtures (NaCl-NaBr-NaNO 3 ) deposited on the walls of a Teflon chamber at 298 K. The films were generated by nebulizing aqueous 0.25 M NaNO 3 solutions which had NaCl and NaBr added to vary the mole fraction of halide ions. Molar ratios of chloride to bromide ions were chosen to be 0.25, 1.0, or 4.0. The subsequent generation of gas phase NO 2 and reactive halogen gases (Br 2 , BrCl and Cl 2 ) were monitored with time. The rate of gas phase NO 2 formation was shown to be enhanced by the addition of the halide ions to thin films containing only aqueous NaNO 3 .] r 1.0, the NO 2 enhancement was similar to that observed for binary NaBr-NaNO 3 mixtures, while with excess chloride NO 2 enhancement was similar to that observed for binary NaCl-NaNO 3 mixtures. Molecular dynamics simulations predict that the halide ions draw nitrate ions closer to the interface where a less complete solvent shell allows more efficient escape of NO 2 to the gas phase, and that bromide ions are more effective in bringing nitrate ions closer to the surface. The combination of theory and experiments suggests that under atmospheric conditions where nitrate ion photochemistry plays a role, the impact of other species such as halide ions should be taken into account in predicting the impacts of nitrate ion photochemistry.

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Section: Discussionmentioning

confidence: 99%

Production of gas phase NO2 and halogens from the photolysis of thin water films containing nitrate, chloride and bromide ions at room temperature

Richards-Henderson

Callahan

Nissenson

et al. 2013

Phys. Chem. Chem. Phys.

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“…3.3) and this parameter needs thus to be assumed so that simulation results match observations. Interestingly, a recent re-run of a specific nitrate snow-chemistry model where the liquid fraction was reduced by a factor of up to 100 showed that the overall results were surprisingly robust and only slightly sensitive to the assumed volume of the liquid fraction, when other parameters -such as solubility limitswere accounted for and concentrations adjusted (Bock and Jacobi, 2010;Jacobi, 2011).…”

Section: Chemical Processes In Modelsmentioning

confidence: 99%

“…Reactive species are localised in a liquid environment with a constant volume that takes concentration enhancements due to the reduced volume of this liquid fraction into account. A similar approach was used to reproduce laboratory experiments investigating the photolysis of nitrate in snow (Honrath et al, 2000;Dubowski et al, 2002;Jacobi and Hilker, 2007;Bock and Jacobi, 2010;Jacobi, 2011). Over time the applied chemical mechanisms were upgraded from very simplified mechanisms as presented by Liao and Tan (2008) to the most advanced model to date presented by Thomas et al (2011).…”

Section: Conclusion About Chemistrymentioning

confidence: 99%

“…A key issue is the distribution of impurities. For example, most of the described models including chemical reactions assume that these reactions take place in a liquid environment in the snow matrix (Michalowski et al, 2000;Boxe and Saiz-Lopez, 2008;Bock and Jacobi, 2010;Thomas et al, 2012). This approach seems well justified when liquid brine is present.…”

Section: Synthesis and Outlookmentioning

confidence: 99%

“…Some experiments indicated that the concentrations in such a brine fraction can be deduced assuming a simple thermodynamic equilibrium approach using ideal behaviour of the solutes (Cho et al, 2002). Therefore, such an approach to define initial concentration of solutes in a given volume of brine has been used by Boxe and Saiz-Lopez (2008) and during further studies based on laboratory experiments (Jacobi and Hilker, 2007;Bock and Jacobi, 2010;Jacobi, 2011). A recent study refined this approach, taking into account the non-ideal behaviour of the solutes in the highly concentrated brine (Kuo et al, 2011), leading to a better agreement with previous laboratory experiments.…”

Section: Synthesis and Outlookmentioning

confidence: 99%

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A review of air–ice chemical and physical interactions (AICI): liquids, quasi-liquids, and solids in snow

et al. 2014

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Abstract. Snow in the environment acts as a host to rich chemistry and provides a matrix for physical exchange of contaminants within the ecosystem. The goal of this review is to summarise the current state of knowledge of physical processes and chemical reactivity in surface snow with relevance to polar regions. It focuses on a description of impurities in distinct compartments present in surface snow, such as snow crystals, grain boundaries, crystal surfaces, and liquid parts. It emphasises the microscopic description of the ice surface and its link with the environment. Distinct differences between the disordered air–ice interface, often termed quasi-liquid layer, and a liquid phase are highlighted. The reactivity in these different compartments of surface snow is discussed using many experimental studies, simulations, and selected snow models from the molecular to the macro-scale. Although new experimental techniques have extended our knowledge of the surface properties of ice and their impact on some single reactions and processes, others occurring on, at or within snow grains remain unquantified. The presence of liquid or liquid-like compartments either due to the formation of brine or disorder at surfaces of snow crystals below the freezing point may strongly modify reaction rates. Therefore, future experiments should include a detailed characterisation of the surface properties of the ice matrices. A further point that remains largely unresolved is the distribution of impurities between the different domains of the condensed phase inside the snowpack, i.e. in the bulk solid, in liquid at the surface or trapped in confined pockets within or between grains, or at the surface. While surface-sensitive laboratory techniques may in the future help to resolve this point for equilibrium conditions, additional uncertainty for the environmental snowpack may be caused by the highly dynamic nature of the snowpack due to the fast metamorphism occurring under certain environmental conditions. Due to these gaps in knowledge the first snow chemistry models have attempted to reproduce certain processes like the long-term incorporation of volatile compounds in snow and firn or the release of reactive species from the snowpack. Although so far none of the models offers a coupled approach of physical and chemical processes or a detailed representation of the different compartments, they have successfully been used to reproduce some field experiments. A fully coupled snow chemistry and physics model remains to be developed.

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Major fraction of black carbon is flushed from the melting New Hampshire snowpack nearly as quickly as soluble impurities

et al. 2017

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Seasonal snowpacks accumulate impurities derived from atmospheric aerosols and trace gases throughout the winter and release them during snowmelt. Previous field and laboratory studies have shown that a snowpack can lose up to 80% of the soluble ion burden in the first 20% of the melt, an event commonly known as an ionic pulse. Other studies have concluded that particulate impurities (e.g., black carbon (BC)) concentrate in surface layers during melt which can have important implications for snowpack albedo. However, model and field studies have indicated that meltwater scavenging efficiency of BC in melting snowpacks is still an area of uncertainty. To quantify BC melt dynamics and the release of soluble impurities, we collected and analyzed near‐daily chemical profiles in the snowpack at three sites during two winters in New Hampshire, United States of America. We observe an ionic pulse and a pulse of BC from the snowpack at the onset of melt; up to 62% of BC leaves within the first 24% of the melt. Surface concentrations of BC are higher than seasonal medians at the end of the winter season, but surface enhancements do not appear to be closely linked to decreases in snow‐water equivalence caused by melting.

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Development of a Mechanism for Nitrate Photochemistry in Snow

Cited by 42 publications

References 64 publications

Production of gas phase NO2 and halogens from the photolysis of thin water films containing nitrate, chloride and bromide ions at room temperature

Production of gas phase NO2 and halogens from the photolysis of thin water films containing nitrate, chloride and bromide ions at room temperature

A review of air–ice chemical and physical interactions (AICI): liquids, quasi-liquids, and solids in snow

Major fraction of black carbon is flushed from the melting New Hampshire snowpack nearly as quickly as soluble impurities

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